The World Health Organization (WHO) says there is no risk from low level, long-term exposure to wi-fi networks and the United Kingdom's Health Protection Agency reports that exposure to Wi-Fi for a year results in the same amount of radiation from a 20-minute mobile phone call.

A small percentage of Wi-Fi users have reported adverse health issues after repeat exposure and use of Wi-Fi, though there has been no publication of any effects being observable in double-blind studies. A review of studies involving 725 people that claimed electromagnetic hypersensitivity found no evidence for their claims.

International guidelines on exposure levels to microwave frequency EMFs such as ICNIRP limit the power levels of wireless devices and it is uncommon for wireless devices to exceed the guidelines. These guidelines only take into account thermal effects, as nonthermal effects have not been conclusively demonstrated. The official stance of the British Health Protection Agency is that there is no consistent evidence to date that WiFi and WLANs adversely affect the health of the general population, but also that it is a sensible precautionary approach to keep the situation under ongoing review.

Most wireless LAN equipment is designed to work within predefined standards. Wireless access points are also often close to humans, but the drop off in power over distance is fast, following the inverse-square law. However, wireless laptops are typically used close to humans. WiFi has been anecdotally linked to electromagnetic hypersensitivity, e.g., in Toronto, Canada schoolchildren as well as staff workers of France National Library.

The HPA's position is that radio frequency (RF) exposures from WiFi are likely to be lower than those from mobile phones. It also saw no reason why schools and others should not use WiFi equipment. In October 2007, the HPA launched a new systematic study into the effects of WiFi networks on behalf of the UK government, in order to calm fears that had appeared in the media in a recent period up to that time. Dr Michael Clark, of the HPA, says published research on mobile phones and masts does not add up to an indictment of WiFi. Wireless devices can emit even more radiation than mobile phones.

dBm is an abbreviation for the power ratio in decibels (dB) of the measured power referenced to one milliwatt (mW). It is used in radio, microwave and fiber optic networks as a convenient measure of absolute power because of its capability to express both very large and very small values in a short form.

A Faraday cage or Faraday shield is an enclosure formed by conducting material or by a mesh of such material. Such an enclosure blocks external static and non-static electric fields. Faraday cages are named after the English scientist Michael Faraday, who invented them in 1836.

See also:
Wi-Fi
Wireless Electronic Devices and Health
Non-Ionizing Radiation
Electromagnetic Hypersensitivity

Source: Wikipedia (All text is available under the terms of the Creative Commons Attribution-ShareAlike License)